For the love of god don't buy from Eclipse!!!

Their customer service is horrendous and you'd be better off flushing your money down the toilet. I ordered from them a few years ago (their service hasn't got any better trust me, there are complaints scattered around various forums I frequent) and 90% of my order was either faulty, broken or simply not there.
When I paid them a visit in person to return everything, they were rude and didn't even offer an apology. Needless to say I asked for a complete refund and will NEVER buy anything from them again.
You're far better off going with a well know company like HP, Dell or perhaps Scan (not sure if they do laptops actually). I'd recommend spec'ing up a laptop on Dells site and give them a call once you have the spec printed out in your hand. Haggle with 2-3 people over the phone asking for the best price they can give you.
I do this for friends/family and on average save £300-£400 off the website price. The trick is to ask for every conceivable extra (insurance, RAM upgrades etc) and then start asking for money off as well, be cheeky the worst they can say is no. They will want you CC details to send you a quote which is fine because they can't authorise the build process without a written email from you saying to go ahead. Play them off against each other and you WILL save £££'s. PM me if you want some more advice.
Oh, to address your orignal question, I'd say stick with XP if you do anything remotely unusual with your laptop. If you're just web surfing, watching movies and word processing go with Vista.